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Ultrafast glutamate sensors resolve high-frequency release at Schaffer collateral synapses

Helassa, Nordine, Durst, Celine, Coates, Catherine, Kerruth, Silke, Arif, Urwa, Schulze, Christian, Wiegert, J. Simon, Geeves, Michael A., Oertner, Thomas, Torok, Katalin and others. (2018) Ultrafast glutamate sensors resolve high-frequency release at Schaffer collateral synapses. Proceedings of the National Academy of Sciences, . ISSN 1091-6490. (doi:10.1073/pnas.1720648115)

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Abstract

Glutamatergic synapses display a rich repertoire of plasticity mechanisms on many different time scales, involving dynamic changes in the efficacy of transmitter release as well as changes in the number and function of postsynaptic glutamate receptors. The genetically encoded glutamate sensor iGluSnFR enables visualization of glutamate release from presynaptic terminals at frequencies up to ?10 Hz. However, to resolve glutamate dynamics during high-frequency bursts, faster indicators are required. Here, we report the development of fast (iGluf) and ultrafast (iGluu) variants with comparable brightness but increased Kd for glutamate (137 ?M and 600 ?M, respectively). Compared with iGluSnFR, iGluu has a sixfold faster dissociation rate in vitro and fivefold faster kinetics in synapses. Fitting a three-state model to kinetic data, we identify the large conformational change after glutamate binding as the rate-limiting step. In rat hippocampal slice culture stimulated at 100 Hz, we find that iGluu is sufficiently fast to resolve individual glutamate release events, revealing that glutamate is rapidly cleared from the synaptic cleft. Depression of iGluu responses during 100-Hz trains correlates with depression of postsynaptic EPSPs, indicating that depression during high-frequency stimulation is purely presynaptic in origin. At individual boutons, the recovery from depression could be predicted from the amount of glutamate released on the second pulse (paired pulse facilitation/depression), demonstrating differential frequency-dependent filtering of spike trains at Schaffer collateral boutons.

Item Type: Article
DOI/Identification number: 10.1073/pnas.1720648115
Uncontrolled keywords: glutamate, synaptic transmission, post-tetanic potentiation, hippocampus, two-photon imaging
Divisions: Faculties > Sciences > School of Biosciences
Depositing User: Michael Geeves
Date Deposited: 14 May 2018 12:21 UTC
Last Modified: 29 May 2019 20:32 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/67010 (The current URI for this page, for reference purposes)
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